The following background information may present examples of specific aspects of the prior art (e.g., without limitation, approaches, facts, or common wisdom) that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon. Neurosurgery routinely involves performing craniotomies for exposure of the brain and intracranial contents for various intracranial pathologies including, but not limited to, tumors, head injuries, vascular malformations, aneurysms, infections, hemorrhages, strokes, and brain swelling. A craniotomy typically involves the creation of burr holes and the removal of a portion of the skull (i.e., bone flap) with subsequent healing of the bone flap for closure.
By way of educational background, an aspect of the prior art generally useful to be aware of is that several methods and fixation devices are currently available for re-attaching the bone flap to the skull including small metallic or absorbable plates with screws or wires. Another current method is the use of cranial clamps consisting of two connected circular elements placed on the inside and outside surfaces of the skull. The aforementioned cranial fixation devices generally provide for a rigid fixation of the bone flap to the skull.
In cases of post-operative intracranial hemorrhaging and/or the development of brain swelling, a decompressive craniectomy is typically performed. A decompressive craniectomy is a neurosurgical procedure generally used to treat increased pressure within the skull, herein referred to as intracranial pressure (ICP), from causes such as, but not limited to, head injury, stroke, brain tumor, infection, cerebral hemorrhage, space occupying lesions, hypoxia, hypertension, aneurysm, arteriovenous malformation, venous sinus thrombosis, craniosynostosis, and hydrocephalus. The technique of performing a decompressive craniectomy often involves the removal of a portion of the skull and opening of the dura mater covering the brain, thereby allowing the swollen brain to herniate outwards through the surgical skull defect rather than downwards to compress the brainstem. The procedure generally improves outcomes by lowering ICP. Increased ICP is often debilitating or fatal because this pressure may result in compression of the brain and restriction of cerebral blood flow. A typical aim of a decompressive craniectomy is to reduce this pressure. In general, it is believed that the larger the bone flap, the more ICP is reduced. Following removal of the bone flap, the dural opening is typically closed with a patch graft taken from a cow, pig, cadaver, or a synthetic graft. A synthetic collagen matrix is often used as a graft since the matrix is capable of expanding. In addition to reducing ICP, studies typically have shown that a decompressive craniectomy may improve cerebral perfusion pressure and cerebral blood flow in patients with head injuries. A decompressive craniectomy may also be used in some cases to treat major strokes associated with malignant brain swelling and increased ICP. It is believed that a decompressive craniectomy typically improves survival and functional outcome in patients with severe brain swelling from causes such as, but not limited to, head injury or stroke if performed in a timely manner. There usually is an inherent time delay between diagnosing the cause of the increased ICP and performing a decompressive craniectomy. Typically, once a post-operative increase in ICP is detected, either through a clinical exam or an ICP monitoring device, medical treatment is initiated and CT or MRI imaging is obtained to identify the underlying cause of the increased ICP. If the need for another surgery or a decompressive craniectomy is identified, the anesthesiologist and operating room staff are notified and surgery is generally performed as promptly as possible. Unfortunately, at times the operating room and/or staff are unavailable, which may increase the time before the surgery can be performed. Despite the best of attempts by the surgeon, in some cases of massive brain swelling or a rapidly developing post-operative hemorrhage, this delay may result in irreversible brainstem injury and in some cases a consequent vegetative state or death.
After a craniectomy, it is believed that the risk of brain injury is increased because of the removed bone flap, particularly after the patient heals and becomes mobile again. In addition, there is often an obvious cosmetic skin deformity. Therefore, special measures are generally taken to protect the brain, such as, but not limited to, a helmet or a temporary implant in the skull. Other risks that may arise out of a craniectomy include, without limitation, infection, cerebrospinal fluid leakage, hydrocephalus, encephalomyocele, subdural hygroma and hemorrhage.
Once the patient has healed sufficiently, the craniectomy skull defect is usually closed with a cranioplasty. A cranioplasty typically involves the repair of a defect in the vault of the skull. This repair may be carried out by using bone removed in an earlier surgery that has been preserved or by using bone from elsewhere as a graft. Bone that may be used as a graft may include, without limitation, the iliac bone bounding the pelvis, ribs or a portion of adjacent skull bone. If possible, the original bone flap is generally preserved after the craniectomy in anticipation of the cranioplasty. The bone flap is usually stored sterilely in a freezer until the patient is ready for implantation of the bone flap into the craniectomy skull defect. Typically, this time period can last several months since it may take this long to treat the underlying cause of the increased ICP. This extended time period may result in the increased risk of brain injury and may also cause an increased risk of infection in the stored bone flap. Another technique of storing a removed bone flap typically involves placing the bone flap under the skin in the abdomen of the patient. This technique generally requires a surgical procedure to place the bone flap in the abdomen and another surgical procedure to remove the bone flap, thereby typically increasing consequent risks to the patient. In cases where the bone flap cannot be replaced due to infection or any other reason, the skull defect is generally repaired with a prosthetic plate or titanium mesh and bone cement. A prosthetic plate typically cannot completely replicate the original skull defect, and therefore some cosmetic deformity often persists following a prosthetic cranioplasty. The prosthesis may also increase the risk of infection. The risks associated with cranioplasty typically include, without limitation, infection, hemorrhage, brain injury, seizures, and death along with other risks inherent to any surgery and general anesthesia. It is also usually necessary for the patient to remain in the hospital for a week or so after a cranioplasty.
By way of educational background, another aspect of the prior art generally useful to be aware of is that some cranial fixation devices describe their use for distraction osteogenesis. Distraction osteogenesis is a surgical process used to reconstruct craniofacial deformities. The bone is fractured into two segments, and the two bone ends of the bone are gradually moved apart during the distraction phase, allowing new bone to form in the gap and reshape the length of the bone. When the desired length is reached, a consolidation phase follows in which the bone is allowed to solidify in the gap. For example, without limitation, one such device describes a telescopic bone plate for use in bone lengthening by distraction osteogenesis. The bone plate is attached to osteomically separated mandible or skull sections by a thread screw assembly. The extent of the required distraction can be adjusted by an external screwdriver. Another such device describes a skull fixation device typically used for the treatment of craniofacial deformities that provides for relative movement of the skull segments by a percutaneously placed external wrench. Yet another such device describes a mandible or skull expansion plate. The extent of the expansion is adjusted by an externally placed device. Another currently available skull expansion plate comprises a hinged plate at one end and a bone adjuster at the other end comprising two plates with a shaft. The shaft is operated externally to adjust the distance between the bone flap and the skull.
The aforementioned cranial fixation devices in the prior art provide for treatment of craniofacial defects, in particular craniosynostosis. These devices generally require an external screwdriver or other external adjustment means to control the extent of the skull movement allowed and do not typically describe or provide for outward or inward movement of the bone flap relative to the skull in response to a change in the ICP. These devices are also generally placed on the outer surface of the skull and have substantially high profiles which may result in increasing the risk of scalp irritation and palpable cosmetic deformities. One can expect that chronic scalp irritation may cause erosion and exposure of the device through the skin with consequent life threatening infections.
By way of educational background, another aspect of the prior art generally useful to be aware of is that there are multiple methods for performing a decompressive craniectomy. One method of performing a decompressive craniectomy involves attaching the bone flap to the skull with a hinged plate. This method describes attaching the hinged plate to one end of the bone flap and attaching the other end of the bone flap to a rigid plate or no plate at all. The described method typically involves another surgery to fixate the unconstrained bone flap at the rigid plate or plate free end to the skull once the brain swelling subsides. Another method describes a deformable plate which may be used instead of a hinged plate as the bone flap attachment. This construct also typically involves another surgery to fixate the unconstrained bone flap at the straight plate or plate free end of the bone flap. The end of the bone flap attached to the hinged or deformable plate is generally unable to move outwards, and therefore allows limited bone flap movement. Another method involves the use of a two part, sliding device for cranial fixation. This device protrudes outwards from the skull surface and may result in a cosmetic defect, overlying skin irritation, risk of erosion or infection, and typically requires another operation to remove the device once the bone flap heals to the skull.
In view of the foregoing, it is clear that these traditional techniques are not perfect and leave room for more optimal approaches.